These strata are of great thickness, and have numerous outcrops
that permit of their being worked by quarrying.
These itabirites present themselves under two very distinct aspects and
offer a certain difference in their composition. Some are essentially
friable, and are called by the vulgar name of _jacutingaes_. It is
this variety (which is the one most easily mined) that is principally
consumed in the forges. The others, on the contrary, are compact.
Their exploitation is more difficult, and before putting them into the
furnaces it is necessary to submit them to breakage and screening; so
the use of them is more limited.
The first variety contains less iron and more gangue, but, _per contra_,
possesses much oxide of manganese. The second, on the contrary, is
formed almost wholly of oxide of iron with but little gangue and only
traces of oxide of manganese. The following are analyses of these two
varieties of ore:
_Friable Ore_.
Fe_{2}O_{2}................
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